A doubt on stabilty of temperature measurement

I have a SCXI-1102,and two SCXI-1112 in a SCXI-1000 chassis with a SCXI-1303 terminal block. I connected one thermocouple at Channel 0 in SCXI-1300, and also connected other TCS to SXCI-1112. And I tried to measure ambient temperature by T-type thermocouples. In VI, I set CJC type to be constant value, and it automatically set default temperature at 25 degree cellsius. Then I test it, but temperatures by thermocouples are differert from the value of thermometer. So I changed CJC constant values accordingly, and I testest again, It still did
not show the right value.
BTW: When the data acquire system run for a long time, such as half an hour, does it affect the data
acquired?

Both of the modules you mentioned have built in cjc sensors. You mentioned the 1303 terminal block then later called it a 1300. The 1303 should have a more accurate cjc reference than the 1300. I have not used the 1112 but since it is designed specifically for Thermocouple measurements they should have a decent cjc sensor network. I will mention that the miniconnector plugs should be the right type for the T type you are using but I imagine you have done this.
In the scan mode your 1102 module will continue to scan the cjc so changes in ambient temperature at the chassis should be compensated for. Since the 1112 are newer module they should do the same. Some of the older isolated modules only picked up the cjc reference at on the initialization of the sc
an. I have used the 1102 modules with the 1303 terminal blocks for several years. The accuracy of this combination usually keeps me within a couple deg F. when I check the system.
If you are using the 1303 terminal block make sure you have the right resistor network for your application. Check your documentation for if you have the 10 ohm bias resistor in and your tc is grounded you will see a significant error.
There are ways of using an external CJC to improve your accuracy if needed. These methods will increase the cost of your system, as they will require additional hardware.

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RTD Temperature Measurements using LabView 2013 and MyRio

Hey everyone. I am VERY new to LabView programming and working with a MyRio. I need to figure out how to measure the resistance of a 2 wire RTD to find a temperature utalizing the MyRio and LabView. I am pretty lost on how to do this. Does anyone know some good resources for making the LabView program off of the tops of their heads? I've figured out how to measure from specific pins, but I am not sure how to get it to constantly output a voltage from the output pins.
Eventually, I would like to have it display the temperature as well as have it turn on or off a heater depending on that temperature, but that will come far later in this process. First things first, how do I take temperature measurements utalizing LabView 2013 and a MyRio with a 2 Wire RTD.
Thanks so much!

Hi JoshEpstein87,
The myRIO can't acquire a change in resistance directly, so you'll need to somehow convert the change in resistance to a change in voltage. There are multiple ways to do this, but you'll need to build an external circuit and then read the voltage output with the myRIO. One example of a circuit that allows you to do this can be found here. To output a voltage on the analog output pins, you should just need to set the output voltage and then it will remain at that voltage until you change it or power cycle the myRIO.
To get started with LabVIEW and myRIO programming, see the following page:
http://www.ni.com/myrio/setup/getting-started/
There are some links to LabVIEW training as well as resources about RIO programming. I also highly recommend you check out the myRIO Community as there are example programs on there that you can take a look at to see how they are designed.
Best Regards,
Matthew B.
Applications Engineer
National Instruments

Help needed with temperature measurement

hi guys
I need some help with temperature measurement. I've got a NI PCI 5229 card and a powertransmitter. The power transmitter is programmed to output a 4-20mA (0°C - 100°C) signal. How can i get labview to convert this mA signal to displaying it as temperature? Please include a lot of detail as I am a first time labview user.
Thanx

Hi Jaco,
calculate gain and offset for your values. After you have this values, you can calculate your temperature. See the attached picture.
Hope it helps.
Mike
Message Edited by MikeS81 on 05-18-2008 02:44 PM
Attachments:
Unbenannt1.PNG ‏30 KB

Temperature measurements display incorrectly after opening a project.

Dear All,
I am having some difficulty in setting up LabView SignalExpress version 5.0.0 to display RTD temperature measurements from the NI9217 module and the NI cDAQ-9178.
I have two problems:
1. I cannot set the waveform chart to show the desired time interval; I need to set the time interval displayed on the chart to 30 minutes. This means that before taking 30 minutes of continuous measurement the user would see a fixed grid with fixed time boudaries and the plot moving from the left hand side of the screen to the right hand side of the screen. After thirty minutes of measurements have been taken, the chart would begin to "scroll" so that the earliest measurements move off the screen and the chart still displays the time interval of 30 minutes.
2. I need the chart to display correctly immediately after the project has been opened; When I open the project and click the 'run' button, the windows are all displayed correctly but the readings are not displayed correctly, the chart only displays one short line to the right of the screen and a very short time interval of less than a second. I can correct this by changing to a Time XY Graph and then back to a waveform chart but need this to display correctly as soon as the software is opened. The incorrect and the corrected chart are shown below:
The chart below is displayed when the software is opened and the run button is clicked. This chart style is incorrect because the temperature line is displayed in the bottom right of the chart and only for a short time interval.
The chart below is closer to the required graph described in point 1 but I cannot set the time interval to stay fixed at 30 minutes, nor can I make the software display the graph like this on opening, I always have to switch to a different chart type and then switch back to a Waveform chart to replace the format above with the format below:
Any help would be appreciated,
Thanks,
Matthew

Hi Matthew,
We should be able to used this function to save the graph settings as well. I have just tried it on my system and got it to work. the procedure I undertook was:
Open my Signal Express Project
Turn off x-axis auto scale (Right click on graph >> X Scale >>Auto scale)
Enter Properties (Right click on graph >> Properties)
Select the scales tab
Select 'Relative To' under the Timestamp Type.
Set the min as 0 and the max as 1800...Press OK
View >> Layouts >> Make Current Project Layout Default
Save
In this case I used the Relative Timestamp Type but you can use whatever time stamp you wish. When opening up this project after doing this the graph is formatted as required immediately.
Let me know how you get on with this.
Regards,
Aaron. E
Applications Engineer Team Lead
National Instruments
ni.com/support

Temperature Measurement errror

I am using a DAQ card 6052E, an SCXI 1121 , chasis SCXI 1000 and TBX 1328 for thermocouple and thermistor measuremtns.
I have gone through the process of configuring everything in MAX. However my temperature measurments using a thermocouple gave me a wrong figure of around 70C. To debug this situation I measured the CJC temperature( using a Labview example)which is around 56C ( when in fact the ambient temperature is around 27C.
Why is my CJC temperature wrong ?. Is the CJC broken?
Also, the cable SH32-32 cable assembly ( for connecttion between 1328 and 1121) came without the cable adaptor. Hence I direclty connected the TBX 1328 to the SCXI 1121 it fits perfectly well withut the adaptor. (You can see the december 2000 manual for T
BX 1328
http://digital.ni.com/manuals.nsf/websearch/22B262582673F346862569B300742094?OpenDocument&node=132100_US)
Could that possibly cause any error?
Can someone give me advice as to how to debug this error? Thanks!

I am reffering to the TBX cable adaptor on page 8 of the December 2000 manual of TBX 1328.
I dont seem to have any bent pins.
I tried your suggestion. The voltage doesnt change when the temperature changes.( in fact it is pretty constatnt )
Also in MAX when i try to set up the global channel/task I keep getting an error saying
Minimum Possible voltage value is -5mV and maximum is 5mV. HOwever i know that the SCXI has maximum output of +5V. ( and i have set the gain to 1000 )
I also tested the cable for connections. It seems fine.
I then tried to use a thermistor for temperature measurements. ON the TBX 1328 I connected the 2 ends of the thermistor to the + and - of the Channel 0 input.
Also I connected
EX0+ to CHo+
EX0 - to CH0-
( I d
ont know if this qualifies as a 2 or 4 wire configuration)
Then when I tried to set up a global channel, it told me that the mimum value should be 198C and Maximum 300C.
I doubled checked my jumper settings on the 1121
gain = 1000
Filter = 4hz
Current excitation = 0.15mA.
it is confiuged for " MTEMP' readings. ( i am using it in multipled mode)
I have tried several different sensors but to no avail.
I am at my wits end and dont know what do to. I had called up NI but their suggestions did not work.

SCXI-1328 temperature measurement accuracy

The catalog says temperature accuracy of SCXI-1328 is 0.5C. If I use three thermocouple, does 0.5C uncertainty exist for all results from each thermocouple? Or, only cold junction has 0.5C uncertainty so that all results have the same offset from real value. In latter case, what is the accuracy of temperature measurement?

Hello efour,
0.5 ºC is the accuracy for the Cold Junction Compensation (CJC) for the SCXI 1328 terminal block for temperatures ranging from 15-35 ºC. Each thermocouple measurement would be subject to this factor. That is the only factor from the 1328 that will affect your temperature measurements.
The overall measurement accuracy of your system would be dependent upon what module you have the 1328 block attached to and what data acquisition (DAQ) card you are using. There is an accuracy calculator available on our website. You can reach it at
Accuracy Calculator
http://www.ni.com/advisor/accuracy/
With this tool, you can enter in your DAQ and SCXI card information. It will return the accuracy of each and then the overall system accuracy. It do
esn�t include the terminal block, though.
General information about taking thermocouple measurements can be found at:
Thermocouple Temperature Measurements
http://zone.ni.com/devzone/conceptd.nsf/webmain/4C54819521D3503786256D73006E8BE9?opendocument
Let me know if you have any further questions on this issue.
Scott Romine,
National Instruments

TBX-68T temperature measurement errors

I am using a TBX-68T with a PXI 4351 card to measure the temperature of a steel plate while the plate is undergoing a TIG (electric arc) welding process. To my knowledge (and based on past experience), the device is connected properly in MAX, with the TBX-68T selected as the accessory. In MAX it also passes the tests. Using the built in CJC and specifying a K-type thermocouple at a range of +/-0.625v, MAX reports temperatures of -80C. The temperature remains nearly the same as the range is increased, but if I change the range to +/-3.75v, the temperature suddenly jumps to 100+C. I used the Measure Thermocouple (with accessory).vi that comes with the driver, and it gives me the same readings. Furthermore, when I initiate the TIG welder the card reads extremely negative (-10e9) temperatures.
What is odd, is that I have used these devices for the exact same process in the past and it generated believable results.
How can I fix the current temperature offset problem? Could I have possibly damaged the unit? Is it possible to use the TBX-68T to reliably detect temperature in arc welding process?
Thanks,
William

Hello,
Becasue TIG welding creates a large electrical discharge I am concerned that you may have shorted the card. What kind of isolation did you use to ensure a separation between the TIG process and the temperature measurement? Because the error is read by both your program and MAX it must be either the temperature configuration or the card. Could you try to conduct a simple Voltage measurement with the 4351, lets say a AA battery. You should be able to read 1.5-1.6V. If this works than the card should be fine, (make sure to test all channels that are failing).
If you cannot read the proper voltage on the card, then it is possible that the card will need to be repaired. Please update us so we can help you further.
Thank you
Regards,
CharlesD
Digital MultimetersSchedule a Free 1 Hour LabVIEW Tutorial with an NI Applications Engineer

Which board is good to produce 5v TTL and temperature measurement?

I want to use Labview to control a valve controller,which contects 6 solenoid valves. This instrument accepts 0-5V TTL signals. I need to switch the valves on/off below 1 second. Which Ni board is good for this application as well as temperature measurement I want also?
Thanks a lot for your suggestion.

Sheng,
One of National Instruments E Series multifunction DAQ devices should provide all of the functionality you require. You may want to also consider using SCC signal conditioning for your temperature measurements. With regards to the digital output, you will want to verify that the current drive provided by an E Series device is great enough to control the valve. If it is not, the NI 6509 digital I/O device provides high current drive. Below, I have included links to the appropriate product pages:
E Series Multifunction DAQ
SCC Signal Conditioning
NI 6509 Product Page
Good luck with your application.
Spencer S.

Accurate differential temperature measurements

May I connect my RTD's in series to improve differential temperature measurement accuracy. I currently use an SCC RTD01 together with a DAQCARD. My differential temperatures are in the magnitude of 0.5 - 1.0C.

Tom,
After reading your second post, I realize that you want to couple the RTD's in series. Originally, I thought you wanted to couple the modules in series.
Ok, you can place the RTD's in series, but this will not increase your measurement accuracy. If you decide to experiment with this setup, make sure you provide sufficient current excitation for both RTD's. What will happen is the experimental error you receive at the first thermocouple will be seen by the next RTD in series, so your error will not decrease.
I advise you to try the oversampling idea to increase your accuracy. Here is information regarding this form of accu
racy improvement.
You can use this accuracy calculator to calculate the accuracy of a given SCXI module and compare this value to the measurement accuracy you're seeing with the SCC module.
I hope this helps! Please let me know if the averaging technique helps to increase your accuracy.
Best of Luck,
Joe Des Rosier
National Instruments

What do I need to perform temperature measurement?

I have a 16-channel DAQ Card installed on my laptop. I want to measure temperature at 6 points in a system, along with pressure and flow. I have already written a 16-channel data aq. VI, and tested the pressure transducers and flow meters. What equipment do I need to complete my system, using my exisitng 16-channel DAQ card? 10 channels are being used by other equipment; 6 are reserved for temperature. Do I need some sort of signal conditioning for the Type K thermocouples I am using? Thanks.

Mikehuh,
On our website he have a utility that will walk you through designing a Data Acquisition and Signal Conditioning system specific to the needs of your signal. Just go to http://amp.ni.com/dd/jsp/ddconfig.jsp and enter in the appropriate information. Good luck with your application!"

Erratic Temperature measurements with FP-TC-120

I have two FP-TC-120 modules on a furnace system. When the temperature
reaches a certain level (930°C) my readings become very erratic. I have
shielded all of the tc's and everything else that is connected to the
FP bank to eliminate EMI noise. The interesting thing is that when I
hook another temperature reader in Parallel with the Fieldpoint module,
my readings are normal on both the new reader and Fieldpoint. Without
the parallel reader, the readings will jump all over and abort my
crystal growth runs due to a false high temp alarm. The problem affects
one or more tc's at a time, and is not specific to only one of them.
One time Tc #2 may fail, then next time may be #4. There is no rhyme or
reason. I have been chasing this problem for three weeks to no avail.
Please advise what could be causing this. I have several FP-TC-120
modules on other furnaces that operate with no problems. This is the
first time I have had trouble.

I apologize for the delay. I haven't been working on this system today.
I'm not sure if it is an Omega unit or some other unit, but it is
powered by the computer's USB port. I also have the same effect with
the old mux board that the fieldpoint is replacing. If the Mux board is
attached in parallel with the Fieldpoint, the readings are fine. I
should note that the mux board is not even hooked up to anything other
than the TC's (meaning nothing at all, no power, no PC, just sitting
there with only TC's on it). The C or COM terminals on the Fieldpoint
are not hooked to the power supply common. The erratic readings are
intermittent, and when the power to the heaters is off, the problem
goes away. Meaning, if I heat the oven up manually to 1000°C, and turn
off the heaters, the TC's will read fine. It is only when I am trying
to control the heat that the problem arises. This definitley points to
noise, but as I said, I taken great measures to eliminate the noise. My
next step tomorrow is to ground every thing that can can be grounded
and even replace all TC's with shielded versions (currently I have a
home-made shield set-up with standard TC's). If these do not work, I
may have to look into purchasing, or developing a low pass filter to
eliminate the noise.
Thanks for your help. If you think of anything else, let me know. I
will post the solution when I find it so you know and others may
benefit.
-Mark

Temperature Measurement using Iex Thermistor with PCI 6259

Hello All,
I am having some difficulty measuring temperature using MAX with Iex Thermistor setup, and would like to know if I have missed any thing important. I am using external current excited thermistor with 2 wire configuration and PCI 6259 card with MAX.
This is a channel that was originally configured to Voltage measurement and MAX measures about 900mV from this channel OK, the voltage converts to Temperature to be around 30C. Then I added a new channel and configured it to measure temperature directly using MAX default Iex Thermistor setup. This is when the problem show up: I will get a constant -273C instead of 30C as expected when run the channel in MAX. I must have been doing something wrong here.
Your help is greatly appreciated!
Bryan
Solved!
Go to Solution.

Hi Ravens, thank you for taking the time on this problem. I am sure the issue was not caused by the A, B, C parameters being wrong, as when I ran the channel in MAX, I am getting a constant -273.15 value, and it was not updated as a real measurement.
To your 2nd question, this is a case of measuring 1 thermistor value using the Iex Thermistor method vs. Voltage measurement. If I set it up to measure Voltage directly, I can see the realtime updates of the measurement values of voltage, which converted to Temperature in my VI to be reasonable values of temperature.
Bryan

Temperature measurement usb 6008 with Thermocouple

Hi,
I am trying to measure temperature with type k thermocouple on USB 6008. I set max for measuring voltage, and got 0 voltage with noise. It would be appreciated if you can help me to wire up properly.
Cheers,

Hi,
You are doing the right thing by acquiring your thermocouple data as a voltage. From there, you can convert it to temperature data after the acquisition.
There are two configurations that you can use to connect your thermocouple to the USB device: Differential and Reference Single Ended (RSE). If you use differential, then you would connect one wire to the + channel and the other wire to the - channel. For example, to use AI 0, you would make connections to AI0 (+) and AI4 (-). If you use RSE mode, then you would connect one wire to an analog input channel and the other wire to ground. So for AI0, you would connect the + to AI0 and the - to ground.
More information about these connections is available in the USB 6008/6009 User Guide. Also, here are two links about the different types of configurations you can use as well as thermocouple polarity:
Field Wiring and Noise Considerations for Analog Signals
How Can I Determine What Kind of Thermocouple I Have and the Correct Polarity of Signal Connections ...
Regards,
Hal L.

USB-6341 and Temperature Measurement

Has anyone been able to measure temperature using thermocouples connected to the USB 6341? I have been told the unit does not have CJC, which is surprising to me. From what i see, there exists significant thermal variation when measuring temp with ta 6341. Has anyone come up with a method of using a thermocouple or RTD with a 6341 to measure temp?
Thanks,
Erik

I use the USB 6251 and 6351 to measure thermocouples all the time. There is the issue of the dissimilar metals at the device terminals adding to the measurement so you have to keep the box iso-thermal but that's not a big problem if you're careful. I usually just set the CJC to CONSTANT (25C) but you can dedicate an extra TC to compensation and stick it in a cup of ice water to get better accuracy. You still may not get the accuracy of dedicated TC interfaces but it's good to a degreeC or so and does very well indicating the relative difference between two channels. Wire up a couple TCs and test it out in your own lab before you trust anything though. Environmental noise can be problematic, especially with long wire runs.
Using LabVIEW: 7.1.1, 8.5.1 & 2013

Pool temperature measurements

I am looking for a low cost solution to measure and acquire (Windows XP)my pool and hot tub temperatures, any suggestions would be greatly appreciated.

How about a temperature to frequency converter and use the Printerport or the stereo sound input to read two channels?
just as starting points:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2025/ln/en
http://www.elecdesign.com/Articles/ArticleID/4563/4563.html
and
http://www.analog.com/library/analogDialogue/archives/30-1/digital.html
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

A doubt on stabilty of temperature measurement

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